YARA-L rules: 37

// Copyright 2023 Google LLC. Licensed under Apache-2.0.

rule ioc_hash_prevalence {

  meta:
    author = "Google Cloud Security"
    description = "Detect process/file events that match hashes found in our MISP instance and have low rolling max prevalence"
    rule_id = "mr_58c661e3-e609-4df8-ae36-e85480e62a50"
    rule_name = "IOC Hash Prevalence"
    type = "alert"
    tags = "prevalence, threat indicators"
    assumption = "Assumes MISP data has been ingested into entity graph; this rule can be modified to utilize other TI indicators"
    data_source = "microsoft sysmon"
    severity = "High"
    priority = "High"

  events:
    $process.metadata.event_type = "FILE_CREATION" or $process.metadata.event_type = "PROCESS_LAUNCH"
    $process.target.process.file.sha256 = $sha256

    // derived from events ingested by Google SecOps
    $prevalence.graph.metadata.entity_type = "FILE"
    $prevalence.graph.metadata.source_type = "DERIVED_CONTEXT"
    $prevalence.graph.entity.file.prevalence.day_count = 10
    $prevalence.graph.entity.file.prevalence.rolling_max <= 3
    $prevalence.graph.entity.file.prevalence.rolling_max > 0
    $prevalence.graph.entity.file.sha256 = $sha256

    // Correlates with MISP data; can be modified based on your MISP parser or other TI
    $ioc.graph.metadata.entity_type = "FILE"
    $ioc.graph.metadata.source_type = "ENTITY_CONTEXT"
    $ioc.graph.metadata.product_name = "MISP"
    $ioc.graph.entity.file.sha256 = $sha256

  match:
    $sha256 over 5m

  outcome:
    $risk_score = 85
    $event_count = count_distinct($process.metadata.id)
    // added to populate alert graph with additional context
    $principal_hostname = array_distinct($process.principal.hostname)
    $principal_process_pid = array_distinct($process.principal.process.pid)
    $principal_process_command_line = array_distinct($process.principal.process.command_line)
    $principal_process_file_sha256 = array_distinct($process.principal.process.file.sha256)
    $principal_process_file_full_path = array_distinct($process.principal.process.file.full_path)
    $principal_process_product_specific_process_id = array_distinct($process.principal.process.product_specific_process_id)
    $principal_process_parent_process_product_specific_process_id = array_distinct($process.principal.process.parent_process.product_specific_process_id)
    $target_process_pid = array_distinct($process.target.process.pid)
    $target_process_command_line = array_distinct($process.target.process.command_line)
    // Commented out target.process.file.sha256 because it is already represented in graph as match variable. If match changes, can uncomment to add to results
    $target_process_file_sha256 = array_distinct($process.target.process.file.sha256)
    $target_process_file_full_path = array_distinct($process.target.process.file.full_path)
    $target_process_product_specific_process_id = array_distinct($process.target.process.product_specific_process_id)
    $principal_user_userid = array_distinct($process.principal.user.userid)
    $target_file_sha256 = array_distinct($process.target.file.sha256)
    $target_file_full_path = array_distinct($process.target.file.full_path)

  condition:
    $process and $ioc and $prevalence
}

// Copyright 2023 Google LLC. Licensed under Apache-2.0.

rule okta_mfa_brute_force_attack {

  meta:
    author = "Google Cloud Security"
    description = "Detects a successful login after multiple failed MFA pushes"
    rule_id = "mr_61d8d679-bf4d-4441-bbbb-65f82a37e3c5"
    rule_name = "Okta MFA Bruteforce Attack"
    reference = "https://sec.okta.com/pushfatigueworkflows"
    mitre_attack_tactic = "Credential Access"
    mitre_attack_technique = "Brute Force"
    mitre_attack_url = "https://attack.mitre.org/techniques/T1110/"
    mitre_attack_version = "v13.1"
    type = "Hunt"
    data_source = "Okta"
    severity = "Medium"
    priority = "Medium"

  events:
    $push.metadata.product_name = "Okta"
    $push.metadata.vendor_name = "Okta"
    $push.metadata.event_type = "USER_UNCATEGORIZED"
    $push.metadata.product_event_type = "system.push.send_factor_verify_push"
    $push.network.parent_session_id = $parent_session_id

    $auth.metadata.event_type = "USER_LOGIN"
    $auth.metadata.product_event_type = "user.authentication.auth_via_mfa"
    $auth.metadata.product_name = "Okta"
    $auth.metadata.vendor_name = "Okta"
    $auth.security_result.action = "ALLOW"
    $auth.network.parent_session_id = $parent_session_id

    $push.metadata.event_timestamp.seconds <= $auth.metadata.event_timestamp.seconds

  match:
    $parent_session_id over 15m

  outcome:
    $risk_score = max(35)
    $mitre_attack_tactic = "Credential Access"
    $mitre_attack_technique = "Brute Force"
    $push_target_user_agent = array_distinct($push.network.http.user_agent)
    $push_principal_ip = array_distinct($push.principal.ip)
    $push_principal_ip_country = array_distinct($push.principal.ip_geo_artifact.location.country_or_region)
    $push_principal_ip_state = array_distinct($push.principal.ip_geo_artifact.location.state)
    //$push_principal_ip_city = array_distinct($push.principal.location.city)
    $push_principal_user_email_addresses = array_distinct ($push.principal.user.email_addresses)
    $push_security_result_summary = array_distinct($push.security_result.summary)
    $push_target_user_email_addresses = array_distinct($push.target.user.email_addresses)
    $push_target_user_userid = array_distinct($push.target.user.userid)
    $push_security_result_risk_reason = array_distinct($push.security_result.detection_fields["Risk Reasons"])
    $dc_push_network_session_id = count_distinct($push.network.parent_session_id)
    $auth_target_user_agent = array_distinct($auth.network.http.user_agent)
    $auth_principal_ip = array_distinct($auth.principal.ip)
    $auth_principal_ip_country = array_distinct($auth.principal.ip_geo_artifact.location.country_or_region)
    //$auth_principal_ip_state = array_distinct($auth.principal.ip_geo_artifact.location.state)
    //$auth_principal_ip_city = array_distinct($auth.principal.location.city)
    $auth_principal_user_email_addresses = array_distinct ($auth.principal.user.email_addresses)
    $auth_security_result_summary = array_distinct($auth.security_result.summary)
    $auth_target_user_email_addresses = array_distinct($auth.target.user.email_addresses)
    $auth_target_user_userid = array_distinct($auth.target.user.userid)

  condition:
    #push > 4 and $auth
}